Currently used pressure sensors include piezoresistive pressure sensors, piezoelectric pressure sensors, capacitive pressure sensors, potentiometric pressure sensors, inductance-bridge pressure sensors and strain gauges, etc. Among of these types of pressure sensors, capacitive pressure sensors have attracted more and more attentions in market because they have a relatively high sensitivity; and they are not easy to be affected by external environments, etc.
Conventional capacitive pressure sensors have some limitations, such as relatively large size, relatively complex fabrication processes and inconvenient operations, etc. In order to overcome these issues, a micro-electro-mechanical system (MEMS) technology has been introduced to form capacitive pressure sensors. The capacitive pressure sensors formed by the MEMS technology may have a plurality of advantages, such as small size, mass production, low cost, and high accuracy, etc. Further, the capacitive pressure sensors formed by the MEMS technology can be integrated with their control circuits on a same substrate, thus weak output signals from the capacitive sensors can be processed at nearby locations. Therefore, electromagnetic interferences to the capacitive pressure sensors may be prevented, and the liability of signal transformations may be improved.
FIG. 1 illustrates an existing capacitive pressure sensor formed by the MEMS technology.
As shown in FIG. 1, the capacitive pressure sensor includes a semiconductor substrate 10 and a doping region 14 in the semiconductor substrate 10. The doping region 14 is configured as a bottom electrode of a planar capacitor. The capacitive pressure sensor also includes a membrane 13 formed above the doping region 14. The membrane 13 is configured as a top electrode of the planar capacitor. Further, the capacitive pressure includes a base 11 configured to support the membrane 13. Further, the capacitive pressure sensor also includes a chamber 12 between the doping region 14 and the membrane 13. The membrane 13, the doping region 14 and the chamber 12 form the planar capacitor. Further, the capacitive pressure sensor also includes a control circuit (not shown) in the base 11. The control circuit connects with the planar capacitor.
When a pressure is applied on the membrane 13 of the planar capacitor, or the inside of the membrane 13 and the outside of the membrane 13 has a pressure difference, the center of the membrane 13 is deformed, thus the capacitance of the planar capacitor is changed. The capacitance change of the planar capacitor can be detected by the control circuit, and the pressure change is obtained. The capacitance of the planar capacitor can be calculated by an equation (1): C=εS/d. “ε” is a dielectric constant of the dielectric material filled in the chamber 12. “S” is an overlap area of the membrane 13 and the doping region 14. “d” is a distance between the membrane 13 and the doping region 14. A relationship between the capacitance change of the capacitor (ΔC=C−C) and a detected pressure can be described by an equation (2): F=PA=Kd0(ΔC)/C0. “F” is an elastic force measured by the planar capacitor. “K” is a spring constant of the membrane 13. “d0” is an initial distance between the membrane 13 and the doping region 14. “C0” is an initial capacitance of the planar capacitor. Thus, it is convenient to obtain the force F by sensing the capacitance change of the planar capacitor using the control circuit.
However, the sensitivity of the capacitive pressure sensor may be relatively low; and the capacitive pressure sensor may occupy a relatively large area of a semiconductor substrate. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.